1. Field of the Invention
The present invention relates to a camera having an automatic magnification adjusting (hereinafter referred to as auto zoom) function and particularly to a camera having an auto zoom function which enables control of auto zoom operation at the will of a photographer.
2. Description of the Related Art
A camera with an auto zoom function of interest to the present invention is described for example in Japanese Patent Laying-Open No. 63-220118.
According to Japanese Patent Laying-Open No. 63-220118, when a ratio of an object size to an image frame (corresponding to a photographing magnification) is preset to a predetermined value, the camera automatically adjusts a focal length and sets a ratio of the object occupied in the image frame to the above mentioned value. In consequence, the user can take a picture in which the ratio of the desired object to the image frame is set to the predetermined value, only by tracking the object without taking notice of zoom operation.
The conventional camera having the auto zoom function is thus constructed. In such a camera, auto zoom operation is started by turn-on of a light measurement switch for light measurement of an object (in most cases, by half depression of a release switch) and even if the light measurement switch is turned off after the start of the auto zoom operation, the zooming continues to a desired zoom position (focal length) in the auto zoom operation. Accordingly, if the user loses interest in the object during tracking the object and turns off the light measurement switch, the zooming still continues. As a result, the timing of the user's operation (the on/off operation of the light measurement switch) and the timing of the operation of the camera (the auto zoom operation) do not agree with each other and the user has a feeling of disagreement in the operation of the camera. In addition, since the camera does not react faithfully to the will of the user, it cannot rapidly proceed to the subsequent operation required by the user and thus it has an inferior responsitivity.
If a tele converter is attached to the lens, a desired auto zoom effect cannot be obtained in auto zoom operation.
If auto zoom operation is to be carried out by using all of measured distance data, it would be sometimes difficult to carry out the auto zoom operation smoothly.
In addition, the conventional camera having the auto zoom function is capable of changing a magnification and it uses a magnification setting method in which selecting means determines a suitable magnification from several magnifications prepared in advance. Accordingly, the camera has a very low degree of freedom in selection of a photographing magnification and it is impossible to change the photographing magnification in auto zoom operation to an arbitrary value.
The auto zoom function is a function of adjusting automatically a focal length f of a taking lens to f=.beta..times.D so that a photographing magnification set to .beta. is obtained with respect to a given distance D to an object. For example, if a picture is to be taken with the camera in a horizontal position, the magnification data is generally selected as described below. It is set to 1/70 in the case of a full-length picture; it is set to .beta.=1/35 in the case of an upper-half body picture; and it is set to .beta.=1/15 in the case of a face picture.